Webster–Ashburton Treaty, (1842), treaty between the U.S. and Great Britain establishing the northeastern boundary of the U.S. and providing for Anglo–U.S. cooperation in the suppression of the slave trade. The treaty established the present boundary between Maine and New Brunswick, granted the U.S. navigation rights on the St. John River, provided for extradition in enumerated nonpolitical criminal cases, and established a joint naval system for suppressing the slave trade off the African coast. The treaty was negotiated by Daniel Webster, at that time secretary of state, and Alexander Baring, 1st Baron Ashburton.

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...to the northwest angle of the Lake of the Woods. The Treaty of Ghent (1814) confirmed this demarcation, although the location of the Maine–New Brunswick boundary remained in dispute until the Webster-Ashburton Treaty of 1842. A convention in 1818 reduced the rights of U.S. fishermen along the shores of the Atlantic colonies and made latitude 49° N (the 49th parallel) the boundary from...

...combination, this time with Tyler. He also hoped to arrange a settlement of the Maine boundary dispute and other controversies with Great Britain. This he succeeded in doing by means of the Webster-Ashburton Treaty (1842), for which he gained popular approval with newspaper propaganda he paid for with secret State Department funds. But he had no chance to realize the dream of a...

...in disputed territory along the Maine–New Brunswick border (the Aroostook War), Van Buren dispatched General Winfield Scott to restore order, and a permanent settlement was negotiated in the Webster-Ashburton Treaty of 1842. In an effort to win the proslavery vote in the election of 1840, Van Buren sided against African slaves on trial in the United States for their part in the Amistad...